This invention relates to rechargeable power cells and more particularly to an improved sealed cell in which the positive electrode is a reoxidizable compound and an oxidizable and ionizable gas is the anodic agent.
Substantial attention has been devoted to the development of several types of electric power cells which employ a gas as one member and a metal oxide, metal hydroxide or oxygen as the other member of the electrochemical couple. One such type is a cell which utilizes an electrochemically reducible compound, e.g., AgO.sub.2, MnO.sub.2, HgO.sub.2, NiOOH or O.sub.2 and a gas that is oxidizable and ionizable, e.g., hydrogen at the anode. A cell of this type which utilizes NiOOH at the cathode is disclosed in U.S. patent application Ser. no. 259,524, entitled "Nickel Hydrogen Fuel Cell", by Dunlop et al filed on June 5, 1972, and assigned to the assignee of this invention. Fuel cells constructed in accordance with the teaching of the Dunlop et al application generally include a positive electrode comprising nickel hydroxide on a conductive support, a negative electrode comprising a catalytic layer such as platinum or palladium on a conductive support and a separator wetted with an electrolyte such as an aqueous KOH solution disposed between the positive and negative electrodes.
Each cell may comprise a single pair but preferably a plurality of pairs of negative and positive electrodes with an electrolyte-wetted matrix or separator between each negative and positive electrode. The electrodes and separators may be disposed in a stacked cylindrical, spiral or other suitable configuration. Whatever the configuration, the assembly of electrodes and separator (s) is disposed in a pressure resistant chamber. The chamber is evacuated and then filled with hydrogen to a selected pressure while the positive electrode is in a discharged state. This allows the cell sufficient hydrogen to provide overdischarge protection. After filling, the cell chamber is hermetically sealed. The cell chamber remains sealed at all times during charging and discharging operations. Cells of this type can be repeatedly charged and discharged without need to add more oxidizable gas to the cell to sustain operation, can operate over a wide range of ambient temperatures, have a relatively high energy density, can be constructed in various configurations, and have inherent overcharge and overdischarge protection.
A disadvantage of this type of cell and other prior art cells which utilize hydrogen as the depolarizer is that the container and feedthroughs used to fill the cell must be specially designed to withstand the relatively high operating pressure and the wide range of pressures over which the cell operates. Typically, such cells operate over a pressure range of 100 to 500 psia at room temperature.
A further disadvantage of such cells is that because the hydrogen is stored as a gas, extreme care must be taken to avoid explosions caused by hydrogen leakage.